Thermophotovoltaic (TPV) energy systems convert thermal energy to electric power using the same principle of operation as solar cells. In particular, a heat source radiatively emits photons which are incident on a semiconductor TPV cell. Photons with an energy greater than the semiconductor bandgap (E.sub.g) excite electrons from the valence band to the conduction band (interband transition). The resultant electron-hole-pairs (ehp) are then collected by metal contacts which can power an electrical load. Photons with energy less than E.sub.g are parasitically absorbed as heat. In order to increase the efficiency of a TPV energy system, some form of spectral control is also employed to reflect the photons with energy less than E.sub.g back to the heat source (radiator) before they are parasitically absorbed.
Due to the low bandgaps (0.4-0.8 eV) and high intensity photon generation rate (&gt;10.sup.23 cm.sup.-3 s.sup.-1) incident on TPV cells, conventional devices (1 cm.sup.2) produce high currents (&gt;4 A/cm.sup.2) and low voltages (&lt;0.5 V). Thus, a large number of series interconnects are required for large power module development. In TPV module development, to-date, series interconnections have been painstakingly made using conventional solar cell paneling techniques. However, a number of novel series interconnect techniques have been made using thin-film microelectronic processing techniques that enable simpler solar cell module fabrication. Similar techniques can also be applied to TPV devices.
These thin film techniques allow the ability to design high-voltage, low-current devices which minimize the number of TPV module series interconnections. In addition, variable current-voltage devices can also be fabricated, which is desirable for TPV applications due to potential temperature and photon-flux variations present within a TPV generator.